Re: Go in gcc 4.7

[Dennis Clarke <dclarke at blastwave dot org>]

> Joel Sherrill <joel.sherrill@oarcorp.com> writes:
>
>> On 01/12/2012 12:16 PM, Andreas Schwab wrote:
>>> Ian Lance Taylor<iant@google.com>  writes:
>>>
>>>> The functions required are makecontext, getcontext, and setcontext.
>>> Note that these functions are obsolescent in POSIX.1-2004 and removed
>>> from POSIX.1-2008.
>> Are there any alternatives? It is bad that Go is already starting
>> out dependent on obsolete methods.  :(
>
> I would be glad to use alternatives but I'm not aware of any.
>
> The getcontext and setcontext functions are easy.  The harder one is
> makecontext.  POSIX appears to be assuming that any use of makecontext
> can be replaced with pthread_create, but if you care about efficiency
> that simply isn't true.
>
> Ian
>

Stuff from the opensolaris project isn't going to help here is it ?


void
makecontext(ucontext_t *ucp, void (*func)(), int argc, ...)
{
	greg_t *reg;
	long *tsp;
	char *sp;
	int argno;
	va_list ap;
	size_t size;

	reg = ucp->uc_mcontext.gregs;
	reg[REG_PC] = (greg_t)func;
	reg[REG_nPC] = reg[REG_PC] + 0x4;

	/*
	 * Reserve enough space for a frame and the arguments beyond the
	 * sixth; round to stack alignment.
	 */
	size = sizeof (struct frame);
	size += (argc > 6 ? argc - 6 : 0) * sizeof (long);

	/*
	 * The legacy implemenation of makecontext() on sparc has been to
	 * interpret the uc_stack.ss_sp member incorrectly as the top of the
	 * stack rather than the base. We preserve this behavior here, but
	 * provide the correct semantics in __makecontext_v2().
	 */
	sp = (char *)(((uintptr_t)ucp->uc_stack.ss_sp - size) &
	    ~(STACK_ALIGN - 1));

	/*
	 * Copy all args to the stack, and put the first 6 args into the
	 * ucontext_t. Zero the other fields of the frame.
	 */
	/* LINTED pointer cast may result in improper alignment */
	tsp = &((struct frame *)sp)->fr_argd[0];
	bzero(sp, sizeof (struct frame));

	va_start(ap, argc);

	for (argno = 0; argno < argc; argno++) {
		if (argno < 6)
			*tsp++ = reg[REG_O0 + argno] = va_arg(ap, long);
		else
			*tsp++ = va_arg(ap, long);
	}

	va_end(ap);

	reg[REG_SP] = (greg_t)sp - STACK_BIAS;		/* sp (when done) */
	reg[REG_O7] = (greg_t)resumecontext - 8;	/* return pc */

}

-- 
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http://pgp.mit.edu:11371/pks/lookup?op=vindex&search=0x1D936C72FA35B44B
+-------------------------+-----------------------------------+
| Dennis Clarke           | Solaris and Linux and Open Source |
| dclarke@blastwave.org   | Respect for open standards.       |
+-------------------------+-----------------------------------+